In the packaging of a waveguide system it is sometimes necessary to change the axial orientation of the waveguide by 90 degrees along the length of a waveguide run. For example, the axial orientation of the waveguide may be required to change from an H-plane orientation to an E-plane orientation or the other way around. For a linearly-polarized antenna, an E-plane is the plane containing the electric field vector in the direction of maximum radiation. An H-plane is the plane containing the magnetic field vector in the direction of maximum radiation. The magnetizing field or H-plane is orthogonal to the E-plane.
The electric field or E-plane determines the polarization and orientation of the radio wave. For a vertically-polarized antenna, the E-plane usually coincides with the vertical/elevation plane and the H-plane coincides with the horizontal/azimuth plane. For a horizontally-polarized antenna, the E-plane usually coincides with the horizontal/azimuth plane and the H-plane coincides with the vertical/elevation plane.
Conventionally, a twist or rotation of the E-field is achieved with an additional curved waveguide section that physically forces the rotation of the orientation of the E-field (and H-field) by 90 degrees as the electro-magnetic (EM) radiation propagates along the length of the curved waveguide. A waveguide that physically forces the rotation of the E-field orientation requires a relatively long waveguide length. Some shorter length twists are currently available. In one example, an additional waveguide section consisting of two quarter wavelength sections orientated at 30 and 60 degrees is placed between the orthogonal waveguides.
Some systems, such as a tightly integrated ferrite switch feed network for an antenna array, require the rotation of an electro-magnetic field from an H-plane orientation to an E-plane orientation to occur within an integrated housing structure, such as a machined aluminum structure. To incorporate such a twist, these assemblies include a feed network that is split into separate E-plane parts, twist parts, and H-plane parts. Thick flanges are required to attach these separate E-plane, twist, and H-plane parts to each other. The positions of the bolts used to attach the various parts must be carefully chosen to ensure the bolt does not protrude into the region of the twisting waveguide.